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/*
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "card_table.h"
#include "base/logging.h"
#include "card_table-inl.h"
#include "gc/heap.h"
#include "gc/space/space.h"
#include "heap_bitmap.h"
#include "runtime.h"
#include "utils.h"
namespace art {
namespace gc {
namespace accounting {
/*
* Maintain a card table from the write barrier. All writes of
* non-NULL values to heap addresses should go through an entry in
* WriteBarrier, and from there to here.
*
* The heap is divided into "cards" of GC_CARD_SIZE bytes, as
* determined by GC_CARD_SHIFT. The card table contains one byte of
* data per card, to be used by the GC. The value of the byte will be
* one of GC_CARD_CLEAN or GC_CARD_DIRTY.
*
* After any store of a non-NULL object pointer into a heap object,
* code is obliged to mark the card dirty. The setters in
* object.h [such as SetFieldObject] do this for you. The
* compiler also contains code to mark cards as dirty.
*
* The card table's base [the "biased card table"] gets set to a
* rather strange value. In order to keep the JIT from having to
* fabricate or load GC_DIRTY_CARD to store into the card table,
* biased base is within the mmap allocation at a point where its low
* byte is equal to GC_DIRTY_CARD. See CardTable::Create for details.
*/
CardTable* CardTable::Create(const byte* heap_begin, size_t heap_capacity) {
/* Set up the card table */
size_t capacity = heap_capacity / kCardSize;
/* Allocate an extra 256 bytes to allow fixed low-byte of base */
UniquePtr<MemMap> mem_map(MemMap::MapAnonymous("card table", NULL,
capacity + 256, PROT_READ | PROT_WRITE));
CHECK(mem_map.get() != NULL) << "couldn't allocate card table";
// All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we
// don't clear the card table to avoid unnecessary pages being allocated
COMPILE_ASSERT(kCardClean == 0, card_clean_must_be_0);
byte* cardtable_begin = mem_map->Begin();
CHECK(cardtable_begin != NULL);
// We allocated up to a bytes worth of extra space to allow biased_begin's byte value to equal
// GC_CARD_DIRTY, compute a offset value to make this the case
size_t offset = 0;
byte* biased_begin = reinterpret_cast<byte*>(reinterpret_cast<uintptr_t>(cardtable_begin) -
(reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift));
if (((uintptr_t)biased_begin & 0xff) != kCardDirty) {
int delta = kCardDirty - (reinterpret_cast<int>(biased_begin) & 0xff);
offset = delta + (delta < 0 ? 0x100 : 0);
biased_begin += offset;
}
CHECK_EQ(reinterpret_cast<int>(biased_begin) & 0xff, kCardDirty);
return new CardTable(mem_map.release(), biased_begin, offset);
}
CardTable::CardTable(MemMap* mem_map, byte* biased_begin, size_t offset)
: mem_map_(mem_map), biased_begin_(biased_begin), offset_(offset) {
byte* __attribute__((unused)) begin = mem_map_->Begin() + offset_;
byte* __attribute__((unused)) end = mem_map_->End();
}
void CardTable::ClearSpaceCards(space::ContinuousSpace* space) {
// TODO: clear just the range of the table that has been modified
byte* card_start = CardFromAddr(space->Begin());
byte* card_end = CardFromAddr(space->End()); // Make sure to round up.
memset(reinterpret_cast<void*>(card_start), kCardClean, card_end - card_start);
}
void CardTable::ClearCardTable() {
// TODO: clear just the range of the table that has been modified
memset(mem_map_->Begin(), kCardClean, mem_map_->Size());
}
bool CardTable::AddrIsInCardTable(const void* addr) const {
return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift));
}
void CardTable::CheckAddrIsInCardTable(const byte* addr) const {
byte* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift);
byte* begin = mem_map_->Begin() + offset_;
byte* end = mem_map_->End();
CHECK(AddrIsInCardTable(addr))
<< "Card table " << this
<< " begin: " << reinterpret_cast<void*>(begin)
<< " end: " << reinterpret_cast<void*>(end)
<< " card_addr: " << reinterpret_cast<void*>(card_addr)
<< " heap begin: " << AddrFromCard(begin)
<< " heap end: " << AddrFromCard(end)
<< " addr: " << reinterpret_cast<const void*>(addr);
}
void CardTable::VerifyCardTable() {
UNIMPLEMENTED(WARNING) << "Card table verification";
}
} // namespace accounting
} // namespace gc
} // namespace art
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